The present research project was carried out to establish the MPR rat as an animal model for human hereditary mucopolysuccharidosis type VI by identifying the mutation responsible for the phenotypes and by examinating therapeutic effects of bone marrow transplantation.We compaired the nucleotide sequences of the rat arylsulfatase B gene by cloning nad sequencing the gene, and found an insertional mutation that causes a fram-shift of the gene. We further revealed that an amplification of the region including the mutation enables to easily identify carriar rats of the mutation.We performed bone marrow transplantation to confirm therapeutic effects of supplement of the normal enzyme producing cells. The recipient rats showed no accumulation of glycosaminoglycan in organs and no urinary excretion of the glycosaminoglycan but partial resoluation of facial dysmorphia and bony feutures, indicating therapeutic effects of the bone marrow transplantation.We, therefore, concluded that the MPR rat is a useful animal model for mucopolysaccharidosis type VI of human.